The emporer's new PDM

So here I sit in my castle with my high blood sugar: 249.

I've also just eaten a sweety, a chocolate covered biscuit; 7g my wife says.

So I use my magnificent new golden PDM to enter a bolus and it says I need zero (0) units:

Suggested bolus: 0.00u
Meal (7/12) = 0.55u
(249-100)/64 = 2.30u
Meal IOB:
(3.60u) = -2.30u
Correction IOB:
(0.55u) = -0.55u
Total = 0.00u

? on my magnificent PDM's 'status' screen shows this:

Insulin on board (IOB)

Meal IOB 3.55u
Correction IOB 0.55u
Total IOB: 4.05u

And I admit I *did* eat a whole lot of chicken, not enough to embarrass Morrison, J. and it wasn't KFC; it was my wife's (CostCo) chicken sprinkled with flour+spices baked; about 4g/piece. The remaining 40g (ok, I ate 8 pieces, please, that's only two chickens) was sweet potatoe (yam.)

My problem here is simple; the meal IOB (3.55u) is fine, the blood sugar maybe isn't fine but that's what I did and it is definitely temporary but I really do need to do the 7g from the biscuit!

Correct me if I'm wrong, but it sounds as if you bolused for everything BUT the biscuit? In that case I'd enter the 7g from the biscuit as an additional bolus.

Yes! That's what I wanted to do, the PDM had a different idea.

I thought I understood the calculations, but my insulin action time really is set to 2 hours, so after 1 hour 20 minutes (which is when I entered the BG of 249 and the 7g carbs) my IOB should have dropped from the original 5.80IU on board after 5:01PM to about .60IU. Where did that 3.60IU IOB come from? (I read it from the status screen of the PDM).

Here's the full time line:
0.40IU bolus (should have disappeared by 2:18PM)
BG 187 mg/dl (actually descending)
bolus 1.35IU (correction)
BG 88 mg/dl (notice the rapid descent)
70g cards (the chicken), requires 5.80IU
bolus 4.60IU (1.20IU of the 5.80IU for the meal comes from the correction)
6:23PM: (82 minutes later - IOB should be 5.8 - 82/120*5.8 = 1.84IU).
7g carbs
BG 249

But the PDM has 3.60IU on board, not 1.84IU! That's actually more like the number it should be subtracting (3.96IU), not the number that remains and it corresponds to a 4 hour (or more) insulin action time, not 2 hours using the calculation on page 143 of the UST400 manual.

The question is, how did the "correction IOB" get to be 0.55IU? At 5:01PM my BG was below the target (100) and so I should have had a negative correction. The 1.35IU correction from 4:46PM should have been cancelled out when it got re-purposed as a meal IOB at 5:01PM and, even if it wasn't, by 6:23PM, 97 minutes later, 1.09IU of that original correction should have been used leaving only 0.25IU, not 0.55IU

Can someone double check my math? I can't see any way of getting 0.55IU out of that timeline.

One update to the time-line; it took me about 25 minutes to enter the blog post, my BG meter shows that the 249BG was actually at 5:55PM (the BG only runs about 90s fast of the PDM).

This explains the calculation:

4:46PM: 1.35IU correction bolus
5:53PM: 0.55IU will remain (after 67min)

So even though the correction bolus has been re-purposed as a meal bolus it remains a correction in the calculation and cancels the subsequent meal bolus. Had the correction originally been entered as a meal bolus it would not have done this (at least this is what page 146 of the manual says!)

my method is pretty simple with the "golden PDM" if I need to bolus and the PDM won't allow me to bolus, then I just ignore IOB, hit bolus, at "enter current bg" I say No, and then when it says "are you going to eat now?" I hit NO. And then I enter the bolus amount that I want it to deliver. So long as it isn't higher than 10 units, it gets delivered and is considered a "meal bolus" not a "correction bolus" even though I don't enter any bg or food amounts. It's not rocket science once you tell it what you want it to do.

I do the same as Clare (and that's what I ended up doing in the above case). If I see that the PDM is double dipping on a correction bolus (? at the screen after confirming the numbers) I back up and tell the PDM to ignore the BG reading. This causes it to actually deliver the required bolus, rather than using an existing correction bolus which it had already used for another meal bolus.

I have to admit I'm tempted to investigate smart phone apps at this point and just use the PDM to deliver boluses:

1) Confirm you are who you are (the bouncing confirm soft button).
2) Wait for the new low range PDM to find the pod.
3) Select 'home' (left soft button).
4) Select 'bolus'
5) Select 'no' (I won't tell you my BG :P)
6) Select 'no' (I won't eat until you work properly :P)
7) Set the bolus amount to the correct number (from the smart phone app)
8) Confirm.

That's an 8 step process, but apart from the bouncing confirm on step 1 and the need to transfer the right bolus from the app it's muscle memory. It doesn't require pressing an option '?' at salient points to ensure the PDM is double dipping so it's probably even safer.